In general, scroll fluid machines include a scroll compressor that compresses a gaseous refrigerant used for a vehicle air conditioner or the like.
In the scroll compressor, a compressing unit accommodated in a housing is formed by joining a fixed scroll in which a spiral wall body is set at one side of an end plate, and a circling scroll in which a spiral wall body is formed in substantially the same shape as that of the wall body of the fixed scroll is set at one side of an end plate.
In the compressing unit of the scroll compressor, a compression chamber is defined by making the side surfaces of the spiral wall bodies of the joined fixed scroll and the circling scroll come into linear contact with each other. The compression chamber is formed so that it can gradually move in the center direction of the spiral with the circling scroll revolving to circle and prevented from rotating.
In other words, in the scroll compressor, by making the circling scroll prevented from rotating revolve to circle around the fixed scroll, the volume of the compression chamber formed between the wall bodies is gradually reduced, thereby compressing the gas in the compression chamber.
In the conventional scroll compressor, a variable circling radius mechanism (such as a slidable variable circling radius mechanism) is used as a gap seal in a radial direction to eliminate a gap between scroll teeth.
The variable circling radius mechanism is formed at a part of the mechanism used to make the circling scroll revolve to circle.
In the variable circling radius mechanism, a driving bush is rotatably mounted in a boss provided at the side of a circle side end plate of the circling scroll via a bearing. In the variable circling radius mechanism, a slide hole elongated in a predetermined direction is formed at an end surface of the driving bush.
A balance weight that cancels an unbalance amount generated when the circling scroll is revolved to circle is fitted to the driving bush.
In the circling scroll, a crankshaft used to transmit a driving force that makes the circling scroll revolve to circle to the driving bush is mounted on a scroll compressor main body.
The crankshaft includes a rotating shaft to which the driving force is entered, and an eccentric shaft projecting from a position eccentric by a predetermined amount from the end of the rotating shaft. By slidably inserting the eccentric shaft into the slide hole of the driving bush, the crankshaft is mounted so as to transmit the driving force.
In the scroll compressor formed in this manner, in conjunction with the movement to revolve the eccentric shaft by rotating and driving the rotating shaft, via the driving bush to which the eccentric shaft is rotatably coupled and a boss linked to the driving bush via a bearing, the circling scroll integrated with the boss revolves to circle.
When the scroll compressor compresses gas, a moment due to the reaction of gas pressure generated when gas is compressed, and a moment due to the centrifugal force of members such as the circling scroll and the balance weight are applied to the eccentric shaft.
Accordingly, in the variable circling radius mechanism of the scroll compressor, by using a vector component of the centrifugal force and the gas pressure force, the circling scroll is moved in a direction (direction in which scroll teeth come close to each other and eliminate a gap) to increase the circling radius, when a driving center of the circling scroll (center of the bearing for the driving bush fitted into a boss hole of the circling scroll) is circled. Subsequently, air tightness is maintained by pushing the circling scroll to the fixed scroll (for example, refer to Patent Document 1).
The variable circling radius mechanism used for the scroll compressor formed in this manner has characteristics that the function of the variable circling radius mechanism can be sufficiently exhibited and the performance thereof can be improved, with the increase of an eccentric amount between the rotating shaft and the eccentric shaft of the crankshaft.
In view of manufacturing a crankshaft to be used here, for example, it is suggested that the crankshaft be manufactured by a compression molding method. In the compression molding method, a plurality of compression molding stations provided with dies and punches for compression molding are prepared, and while delivering a material of the crankshaft across the compression molding stations, the material of the crankshaft is processed by step-by-step cold forging.
In the compression molding method of the crankshaft, at a first step, a main shaft unit with a small diameter is drawn at one end of a material of the crankshaft, and a circular column-like large diameter unit with a predetermined length is formed at the other end of the material.
At a second step, while maintaining the main shaft unit with a die, at a portion eccentric from the main shaft unit at an end surface opposite to the main shaft unit of the large diameter unit, an eccentric shaft unit is formed by punching.
At a third step, while maintaining the eccentric relationship between the two shaft units, the large diameter unit is deformed in a flattening direction, thereby completing the crankshaft (for example, refer to Patent Document 2).
When the crankshaft is manufactured by the compression molding method as described above, it can be manufactured inexpensively. However, if the crankshaft is manufactured by the compression molding method, an increase in the eccentric amount between the rotating shaft and the eccentric shaft is limited in terms of processing.
For this reason, when the eccentric amount between the rotating shaft and the eccentric shaft exceeds the processing limit, not cold forging but hot forging process is applicable for the manufacturing.
When the crankshaft is processed by hot forging, the yield of the product deteriorates due to the occurrence of burr, for example. Accordingly, the manufacturing cost increases, thereby increasing the product cost of the crankshaft.
In the conventional scroll compressor, to rotatably receive the crankshaft, the circular column-like large diameter unit formed between the rotating shaft and the eccentric shaft of the crankshaft is supported by a ball bearing.
Subsequently, in the scroll compressor, when the circling scroll is revolved to circle by the crankshaft, the ball bearing is used to support the crankshaft to prevent the crankshaft from receiving damage. The crankshaft receives damage because the crankshaft is deflected and deformed by an eccentric load applied to the eccentric shaft of the crankshaft, and makes the outer peripheral end of the circular column-like large diameter unit incline and slide. However, ball bearings are expensive.    [Patent Document 1] Japanese Patent Application Laid-open No. H9-105390    [Patent Document 2] Japanese Patent Application Laid-open No. H8-1269